The present invention relates to an electrophotographic image forming apparatus.
(Prior Art)
In an electrophotographic image forming method used in, for example, a copying machine or a printer, generally a photoreceptor to be rotated is electrostatically charged evenly, then, exposure processing corresponding to an image of a document is conducted to form a latent image which is developed by toner, and a toner image thus formed is transferred onto a recording material, thus, the transferred image is fixed on the recording material to be formed as an aimed image.
However, in the process of transferring a toner image, all toner particles on the surface of the photoreceptor are not always transferred onto the recording material completely, and some of the toner particles stay on the surface of the photoreceptor inevitably. A cleaning means is one to remove the residual toner on the surface of the photoreceptor.
Up to now, methods to employ a fur brush roller, a magnetic brush roller or a blade have been typical as a cleaning means, and in particular, a method to use a blade composed of a rubber plate (hereinafter referred to as xe2x80x9crubber bladexe2x80x9d) has been used commonly because it has a simple structure and offers good cleaning results.
Further, in the image forming method stated above, there have been studied various means, for improving reproducibility of fine lines and dots in a formed visible image and for achieving improvement of image quality, and for preventing image defects called black lines on copy and smeared image which are caused by cleaning failure.
For example, when forming an image by fine lines or dots of a digital image, there are used toner particles each has been made small in terms of particle size, for achieving improvement of image quality. As a method to obtain toner particles which have been made small, there is known a method to manufacture toner by means of the so-called polymerization method. However, with respect to toner manufactured by the polymerization method, its particle is closer to a globular shape and is smaller in terms of a diameter, compared with toner particles manufactured by a powdering method. Therefore, it is difficult to remove residual toner on the surface of the photoreceptor sufficiently, resulting in image defects such as background dirt and black lines on copy caused by cleaning failure which easily occur on a visible image to be formed, and this has been a problem.
On the other hand, as a means to make toner itself to be one which can be removed easily, a technology to add fatty acid metal salt such as zinc stearate and calcium stearate to toner has been widely put to practical use, and in this technology, considerable-effects can be obtained even for the toner manufactured by a polymerization method.
However, when toner to which fatty acid metal salt is added is used, a thin film of fatty acid metal salt is formed on the surface of the photoreceptor. Therefore, surface of the photoreceptor is made not to be worn out, paper dust tends to stick to the surface of the photoreceptor, and under the high humidity, image defects called xe2x80x9csmeared imagexe2x80x9d are caused by a flow of electric charges on the surface of the photoreceptor resulted from absorption of moisture in the paper dust.
(Problems to be Solved by the Invention)
An object of the invention is to provide an image forming apparatus capable of forming constantly a visible image with high image quality which is free from image defects, by using specific toner manufactured by a polymerization method and by employing a cleaning means equipped with a brush roller operated under the specific condition, in an electrophotographic image forming apparatus.
The object of the invention mentioned above can be attained by taking the following structures.
An image forming apparatus having the structure in which a latent image formed on a rotating photoreceptor is developed by toner, then, a toner image thus formed is transferred onto a recording material to be fixed thereon, and residual toner on the photoreceptor is removed by a cleaning means, wherein the toner is one that is manufactured through a method in which a polymerizable monomer is polymerized in an aqueous medium, and has a number average particle diameter in a range of 3-8 xcexcm and a shape factor in a range of 0.940-0.985, the cleaning means has therein a rubber blade that comes in contact with the photoreceptor surface and a brush roller that is implanted with brush fibers and is rotated while it is in contact with the photoreceptor under the state of having a linear speed difference against the photoreceptor, and the brush roller has effective rubbing force xe2x80x9cFxe2x80x9d of a brush fiber group touching the photoreceptor that is expressed by the following expression (1) and has a value in a range of 2.5-10.5;
F=nxyEt3/L3xe2x80x83xe2x80x83Expression (1)
Wherein,
xe2x80x9cnxe2x80x9d represents implanted density of brush fibers (bristles/mm2),
xe2x80x9cxxe2x80x9d represents a linear speed difference between the brush fibers and the photoreceptor (mm/s),
xe2x80x9cyxe2x80x9d represents an amount of encroaching (mm) of the brush fiber upon the photoreceptor,
xe2x80x9cExe2x80x9d represents Young""s modulus (kgf/mm2) of the brush fiber,
xe2x80x9ctxe2x80x9d represents a diameter (mm) of the brush fiber, and
xe2x80x9cLxe2x80x9d represents a free length (mm) of the brush fiber.
The image forming apparatus of the invention make it possible to form constantly a visible image with high image quality which is free from image defects, by using toner satisfying the aforementioned conditions and by employing a cleaning means equipped with a brush roller operated under the condition stated above.